1. Field of the Invention
The invention relates to a transmission mechanism and a scanning apparatus using such transmission mechanism to switch output powers.
2. Related Art
In a conventional flatbed scanner, a scanning module is driven by a driving source, such as a motor, to reciprocate back and forth. Usually, the scanning module scans a document at a lower moving speed, and returns to a home position at a higher moving speed after the document is scanned, so that the time spent for the overall scanning process can be shortened. In addition, the moving speed of the scanning module may also be changed according to the scan resolution. Thus, the driving speed of the driving source is preferred to be variable.
In a conventional sheet-fed scanner, it is preferred that the speed at which the documents travel can be varied for high and low scan resolutions.
Often, an additional motor or driving source is employed to execute the switching operation of the power transmission members, such as gears, so that the output power of the power transmission members can be changed. However, the added motor occupies a large space in the scanner, and such scanner fails to achieve a truly compact design.
U.S. Patent Publication No. 2006/0005650 A1 discloses a rocker arm transmission device capable of switching the reduction ratio by changing the position of the rocker arm. In this transmission device, the switching operation is achieved by the meshing between the external teeth of the gears. This switching operation creates great challenges to the precision, strength and durability of the gears.